The recent fix for the AMD FXSAVE information leak had a problematic side effect. It introduced an entry in the x86 features vector which is a bug, not a feature.

The problem with this is that the features vector is designed so that it can be ANDed between CPUs to find out the common feature set. However, bugs aren't features, and bugs should be ORd, not ANDed. In that sense, the *absence* of a bug is a feature.

When I originally wrote the code I always meant to do (b), but never got around to it. It's clear, though, that whatever way we go about this, it should also incorporate the fdiv, hlt, f00f, and coma bugs.